A hybrid vehicle comprises an internal combustion engine as a first drive source and an electric engine as a second drive source. Fuel can be fed to the internal combustion engine from a fuel tank. The electric engine interacts with an electric traction energy accumulator, wherein the electric traction energy accumulator is more intensely discharged in the motor mode of the electric engine and is more intensely charged in the generator mode of the electric engine.
It is already known in practice, depending on defined operating conditions of the hybrid vehicle, to change between a purely electric driving mode, in which only the electric engine provides driving power, a purely internal combustion engine driving mode, in which only the internal combustion engine provides driving power, and a hybrid driving mode, in which both the internal combustion engine and the electric engine provide driving power. It is known in this connection, starting from a purely electric driving mode, to start up the internal combustion engine depending on defined operating conditions. This takes place in the case of hybrid vehicles known in practice when the charging state of the traction energy accumulator is not sufficient to provide the desired driving power solely via the electric engine.
It is furthermore known in practice that when, in a purely electric driving mode of the hybrid vehicle, the internal combustion engine is shut down, a shut-off valve assigned to the fuel tank is closed. This avoids hydrocarbon gas or fuel vapor being able to emerge from the fuel tank and being able to escape into an activated carbon filter or even into the surroundings.
Since, however, a fuel tank is configured merely to a defined pressure, when the pressure in the fuel tank exceeds a limit value, the shut-off valve of the fuel tank has to be opened such that hydrocarbon gas or fuel vapor then escapes into the activated carbon filter or even into the surroundings of the motor vehicle. In particular, hydrocarbon gas or fuel vapor escapes into the surroundings of the motor vehicle whenever the activated carbon filter is already loaded with hydrocarbons to an extent such that said activated carbon filter can no longer absorb any additional loading with hydrocarbons.
U.S. Pat. No. 8,104,454 B2 discloses a method for operating a hybrid vehicle, in which an internal combustion engine is started and fuel vapor is removed from the fuel tank as a function of a first amount of liquid fuel located in a motor vehicle and depending on a first duration of time of a preceding refueling operation. As a function of a second amount of liquid fuel located in the fuel tank and a second period of time since the first refueling operation, fuel vapor is removed from the fuel canister depending on operating conditions of the internal combustion engine.
It is known from DE 102 00 016 B4 to flush a fuel tank of a hybrid vehicle, specifically as a function of a pressure in the fuel tank.
U.S. Pat. No. 9,328,678 B2 discloses a method in which operating conditions of a drive are adapted as a function of a barometric pressure, which is dependent on a change in pressure in a sector of the fuel system.